What Does No Gestational Sac On My Ultrasound Mean?

Possible Reasons for the Absence of a Gestational Sac on Early Ultrasound

Pregnancy ultrasound
What does it mean if a gestational sac can't be seen on an early ultrasound?. Getty Images/Saso Novoselic

What does it mean if you hear that a gestational sac could not be seen on an ultrasound? When is this usually seen, and what are the different reasons why it can't be found on an ultrasound in early pregnancy?

Reasons for No Gestational Sac on An Early Ultrasound

gestational sac is one of the first signs of pregnancy that can be seen on a transvaginal ultrasound (an abdominal ultrasound is much less accurate this early in pregnancy.) It is usually seen on ultrasound by 5 weeks gestational age but is sometimes seen as early as 3 weeks.

The diameter of the sac is around 2 to 3 millimeters and is seen as a white rim around a clear center in your uterus.

If you are also having quantitative pregnancy tests (serum hCG tests) the gestational sac usually becomes visible when hCG levels have reached 1500 to 2000.

Having a gestational sac does not say much about the health of your pregnancy, nor does it say whether an embryo is present or not. The gestational sac is essentially the sac that surrounds the baby (when it becomes visible) and contains amniotic fluid. The next step on ultrasound is usually the appearance of the yolk sac within the gestational sac. The yolk sac functions as nourishment for the developing embryo and can usually be seen by 5.5 to 6 weeks on a transvaginal ultrasound.

If a gestational sac is not seen on an early pregnancy transvaginal ultrasound by around 5 weeks, there are several things that could be occurring.

These include:

  • It is too early for the gestational sac to be visible (wrong dates)
  • The pregnancy is ectopic
  • The pregnancy is a miscarriage

Let's talk about each of these possibilities separately.

It Is Too Early For the Gestational Sac to Be Visible

The gestational sac is typically visible on a transvaginal ultrasound somewhere between three to five weeks of pregnancy, or by the time the hCG has reached 1500 to 2000.

Before that, even in a viable pregnancy, there is not going to be a visible gestational sac on an ultrasound.

If the pregnancy is definitely past 5 weeks, or the hCG level is higher than 2000, a finding of no gestational sac is more likely to indicate a problem. But when there's no confirmation of hCG levels or any definite evidence of the dating of the pregnancy, the pregnancy might still be in very early stages. In this case, a follow-up ultrasound is recommended. This is one of the most common causes of an inability to see a gestational sac on an early ultrasound, especially in the absence of symptoms such as bleeding.

The Pregnancy Is Ectopic

Whenever there is no gestational sac visible in the uterus, there is a possibility of ectopic pregnancy. Ectopic pregnancies (tubal pregnancies) can be life-threatening if not diagnosed before they rupture, so anytime an ultrasound shows no gestational sac, your doctor will likely want to rule out an ectopic pregnancy. This can be frightening, but keep in mind that the absence of a gestational sac is more likely to be related to wrong dates, and even if an ectopic pregnancy is detected, these can be managed well when caught early. An ectopic pregnancy is still a possibility even if you don't have symptoms of an ectopic pregnancy.

A doctor may be able to diagnose ectopic pregnancy and recommend treatment without a follow-up ultrasound if the hCG levels are high enough that the gestational sac would definitely be visible if the pregnancy was located in the uterus. These pregnancies are not always medical emergencies when detected early, and treatment options are not always surgical.

The Pregnancy Is a Miscarriage

If you have experienced early pregnancy bleeding or other miscarriage symptoms, a finding of no gestational sac may mean that you've had a very early miscarriage (chemical pregnancy) or that the pregnancy tissue has already left the uterus.

If there are falling hCG levels along with a finding of no gestational sac, the diagnosis is almost certain to be a miscarriage. As with an ectopic pregnancy, there are different treatment options available if you have a miscarriage.

A Word From Verywell

It can be difficult for doctors to determine right away which of the above explanations is behind a pregnancy with no visible gestational sac. Therefore, it is completely natural to feel concerned and anxious, and perhaps even frustrated. You may be told (or see on medical forms) that you have a "pregnancy of unknown location," which simply means that the ultrasound did not show a gestational sac, and the doctors are not sure whether it is an ectopic pregnancy, a miscarriage, or a very early but otherwise normal pregnancy.

Most likely, you will be asked to come back for a follow-up ultrasound and undergo monitoring of your hCG levels. Together, these repeat tests should give you a clear answer. The wait can be difficult but may be necessary for your doctor to be certain of your diagnosis.

Sources:

Cunningham, F.G., and J Whitridge Williams. Williams Obstetrics. New York: McGraw-Hill Education Medical, 2014. Print.

Richardson, A., Gallos, I., Dobson, S., Campbell, B., Coomarasamy, A., and N. Raine-Fenning. Accuracy of First-Trimester Ultrasound in Diagnosis of Intrauterine Pregnancy Prior to Visualization of the Yok Sac? A Systematic Review and Meta-Analysis. Ultrasound in Obstetrics and Gynecology. 2015. 46(2):142-9.

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